It has been known for some time that fuel cells can be extremely advantageous as power sources, particularly for certain applications, such as a primary source of power in remote areas, with limited service and maintenance facilities, etc. It is of course necessary in such instances that the power system not only be self-contained but be extremely reliable, and in the ultimate have no moving parts.
Various fuel cell systems have thus been devised in the past to accomplish these purposes, but in each case several problems have arisen respecting same. Firstly, in many such systems it has been difficult to control the cell temperatures and to remove waste products produced therein. Cell temperature control is highly significant and further if it is not accomplished with a minimum temperature gradient across the electrodes, uniform current density will not be maintainable, and degradation of the cell will occur. An associated problem has been the inability to continuously supply and distribute the reactant feeds across the electrode surfaces. This problem as well as the problem of removal of waste products each also directly relate to the problem of temperature control, depending upon the particular method employed for waste removal and/or reactant distribution.
One type of fuel cell which has been particularly designed in order to overcome these and other problems is shown and described in U.S. Pat. No. 3,709,736, assigned to the assignee of the present application. This patent describes a fuel cell system which includes a stacked configuration comprising alternating fuel cell laminates and thermally conductive impervious cell plates, the laminates comprising fuel and oxygen electrodes on either side of an electrolyte comprising an immobolized acid. The patentee in that case thus discusses how temperature control, removal of product water, and distribution of oxygen across the cathodes is achieved without the need for an external cooling system, separate coolant fluids, or other such complex devices used in the past. In addition, the use of cooling fins in connection with the cell plates as has also been employed in the past can be eliminated. In the configuration shown in U.S. Pat. No. 3,709,736 the oxidant performs the functions of waste heat removal, product water removal, and supply of oxidant to the cells.
As noted above, the system disclosed in this reference uses an electrolyte comprising an immobilized stable acid, and a typical example of such as electrolyte member is shown and described in U.S. Pat. No. 3,453,149 which utilizes a matrix consisting of a fluorocarbon polymer gel in which the acid electrolyte is entrapped. Inert solid inorganic porous particles are incorporated in the fluorocarbon polymer gel to stabilize the structure. The above noted types of fuel cells have proven to be extremely valuable.
Another type of fuel cell which has also been developed utilizes an ion exchange membrane as the electrolyte between the fuel and oxygen electrodes. For example, U.S. Pat. No. 2,913,511 assigned to General Electric Company discloses use of an ion exchange resin as the electrolyte, i.e. in the form of a membrane separating the electrodes. The configuration employed by this patentee comprises a hydrated ion exchange resin membrane between the electrodes, such that the membrane is substantially saturated with water, and includes a single pair of electrodes and a single ion exchange membrane therebetween as well as means for collecting current from the edges of the electrodes through leads 4 and 5 thereon. Subsequently however in U.S. Pat. No. 3,134,697, again assigned to the General Electric Company, an attempt was made to improve upon such cells. In particular the patentee claims that polarization of the cell can be substantially decreased by a particular combination of electrode and electrolyte structure for such ion exchange resin membrane fuel cells. In particular the patentee teaches integrally bonding and embedding the gas absorbing metal electrolyte member. The patentee teaches however that if the preferred metal powder electrode materials are employed, the electrical conductivity of the electrode is limited and the internal resistance of the cell increased. The patentee thus employs terminal grids contacting the ends of the electrodes for current collection, even in a case where bipolar electrodes are employed with series connection of cells.
A most recent development has been the attempt to employ certain newly developed ion exchange membranes in the latter type of fuel cells. This latest type of electrolyte comprises a NAFION perfluorosulfonic acid membrane recently developed by the DuPont Company. These attempts have thus included preparation of fuel cells which comprise a catalyst layer including a porous metallic collector screen on either side of the ion exchange membrane, with each such catalyst layer imbedded in a porous teflon film in order to prevent moisture from wetting the catalyst surface and thus restricting reactant access thereto. In addition, since this layer is non-conductive, it is necessary to collect the current from the edges of the individual cells in a manner similar to that shown in U.S. Pat. No. 2,913,511 discussed above.
The search has therefore continued for improved fuel cell configurations, and in particular for stacked configurations employing bipolar plates in connection with various ion exchange membranes.